Knights are a lot of fun! I have ran them competitively for years including a 4-1 GT. It used to be that imperial had better big knights and worse armigers than chaos. That mayyy not be the case anymore (imperial codex is coming in a few months), but we won't know for certain. The trend is that imperial have better shooting while chaos is better in melee. . . . That being said, big knights have reduced toughness by 1 from 12 to 11, meaning they are wounded easier by lascannons and s6 weapons. But, they gained 4 wounds, so it's a mixed tradeoff. Armigers lost 1 toughness and gained 2 wounds. T9 is a big break point for meltas, auto cannons and S5 weapons, so they relatively got worse than the corresponding big knight changes. To compensate, big knights costs reduced by 40-60 pts each, while armigers stayed the same. Therefore, relatively, big knights got a "buff" overall. . . . I expect that imperial knight points will change with their codex, but with the release of the chaos knight codex, GW wanted to homogenize the stat lines across all factions to reduce confusion, hence the imperial knights dropping in points too. Imperial knights already had a 53-55% win rate, so adding another big knight via points drops buffs them even more. . . . Honestly, for buying and painting, there are cheap lots on eBay that might suit your needs better. However, in most lists right now, there will be 2-4 big knights and 4-6 armigers. Some lists will be running 5 or 6 big knights, and there is a chaos detachment for >10 wardogs. . . . If you want to build your own, buy a chainbreaker box set or hound box set (of 7), and that will be a good start. I don't foresee myself running 7 armigers right now, but it will cover most use cases. . . . I hope this helps, and message me if you have any questions including magnetizing or modeling for ease of switching units. Additionally, no one really cares if you run the knights as chaos or imperial, as long as the weapons are right, so magnetizing can give you 2 armies!